Genuine question- what do you do to hit that limit? I have the same $30 plan and my phone data usage shows me nearly hitting 2GB a month on average.
The worst instance of abuse was once, for a couple months, I used tethering as my only home Internet access as my land lady was dragging her feet on getting Internet access installed. During one of those months I decided to watch the first few seasons of The Mentalist and that uses data plenty quick. An hour of video is still several hundred MB even with these fancy new encodings.
But if you add in a laptop, things get real ugly, real fast...
Their current deal is $50 for an "unlimited" plan that switches to EDGE after 500MB and $60 for a similar plan with a 2 GB limit (or 3 GB, can't remember which).